Marine corrosion performance of copper alloy UNS C69100

Tungum alloy (UNS C69100) is an aluminium-nickel-silicon brass (chemical composition: 81-84% Cu, 0.70-1.20 Al, 0.8-1.40 Ni, 0.80-1.30 Si, with the remainder Zn) and is reported to have a good corrosion performance in marine environments (fully wetted, splash zone and atmospheric conditions). In order to gain an in-depth understanding of the marine corrosion performance of this alloy, electrochemical test methods including open-circuit potential, electrochemical impedance spectroscopy, potentiodynamic polarization, and zero-resistance ammetry were used for corrosion investigation of UNS C69100 in a 3.5 wt.% sodium chloride aqueous testing solution, in combination with optical microscopy and scanning electron microscopy. The corrosion properties of UNS C69100 obtained by electrochemical methods are also compared to six other alloys: UNS S31603, UNS S31254, UNS S32750, UNS N04400, UNS N08904 and UNS C36000. Galvanic coupling behaviour of UNS C69100 against these six alloys in a 3.5% NaCl solution for 30 days immersion are also reported in this paper

Screen-printed potentiometric Ag/AgCl chloride sensors: Lifetime performance and their use in soil salt measurements

Silver – silver chloride electrodes (Ag/AgCl) for the detection of chloride ions were fabricated using thick-film technology. Five different formulations were prepared and chloride responses were investigated over time. Almost identical and near Nernstian responses were observed over the first 162 days with an average chloride sensitivity for all formulations of -51.12 mV ± 0.45 mV per decade change in chloride concentration compared with a value of -50.59 mV ± 0.01 mV over 388 days for the best two formulations. After 6-months continuous immersion in tap water, pastes formulated with a glass binder began to exhibit a loss in sensitivity whilst those formulated from a commercial thick-film dielectric paste remained functional for the best part of a year. This difference in lifetime performance is attributed to the inclusion of proprietary additives in the commercial paste aiding adhesion and minimising AgCl leaching. The mechanical and chemical robustness of these electrodes has been demonstrated through their ability to detect changing levels of chloride when immersed in soil columns. This particular capacity will make them an invaluable tool in the fields of hydrology, agricultural science, soil science and environmental science

A graphene nanoplatelet-polydopamine molecularly imprinted biosensor for Ultratrace creatinine detection

Accurate and reliable analysis of creatinine is clinically important for the early detection and monitoring of patients with kidney disease. We report a novel graphene nanoplatelet (GNP)/polydopamine (PDA)-molecularly imprinted polymer (MIP) biosensor for the ultra-trace detection of creatinine in a range of body fluids. Dopamine hydrochloride (DA) monomers were polymerized using a simple one-pot method to form a thin PDA-MIP layer on the surface of GNP with high density of creatinine recognition sites. This novel surface-MIP strategy resulted in a record low limit-of-detection (LOD) of 2 × 10^{−2} pg/ml with a wide dynamic detection range between 1 × 10^{−1}-1 × 10^{9} pg/ml. The practical application of this GNP/PDA-MIP biosensor has been tested by measuring creatinine in human serum, urine, and peritoneal dialysis (PD) fluids. The average recovery rate was 93.7–109.2% with relative standard deviation (RSD) below 4.1% compared to measurements made using standard clinical laboratory methods. Our GNP/PDA-MIP biosensor holds high promise for further development as a rapid, accurate, point-of-care diagnostic platform for detecting and monitoring patients with kidney disease

An Investigation into Separation Enhancement Methods for Miniaturised Planar Capillary Electrophoresis Devices

Large structures such as buildings, ships and aircraft often contain numerous components which are exposed to a failure risk due to corrosion processes. Aside from the extra cost of repair and replacement, there are also potential health and safety issues which need to be addressed. Corrosion detection is not a new concept and there exists a variety of methods to detect and evaluate corrosion. The analysis method that is the focus of this work is capillary electrophoresis (CE); commonly used for a number of biological and chemical processes, such as drug, food and water quality analysis, DNA and protein separation and so on. An alternative method to high pressure (or performance) liquid chromatography (HPLC), CE boasts high analysis speeds as well as low limits of detection. Both are of crucial advantage for use in a pharmaceutical market; however the application of CE for in-situ or portable corrosion monitoring has not been investigated in great depth

Characterisation of Crevice and Pit Solution Chemistries Using Capillary Electrophoresis with Contactless Conductivity Detector

The ability to predict structural degradation in-service is often limited by a lack of understanding of the evolving chemical species occurring within a range of different microenvironments associated with corrosion sites. Capillary electrophoresis (CE) is capable of analysing nanolitre solution volumes with widely disparate concentrations of ionic species, thereby producing accurate and reliable results for the analysis of the chemical compositions found within microenvironment corrosion solutions, such as those found at crevice and pit corrosion sites. In this study, CE with contactless conductivity detection (CCD) has been used to characterize pitting and crevice corrosion solution chemistries for the first time. By using the capillary electrophoresis with contactless conductivity detection (CE-CCD) system, direct and simultaneous detection of seven metal cations (Cu2+, Ni2+, Fe3+, Fe2+, Cr3+, Mn2+, and Al3+) and chloride anions was achieved with a buffer solution of 10 mM 2,6-pyridinedicarboxylic acid and 0.5 mM cetyltrimethylammonium hydroxide at pH 4 using a pre-column complexation method. The detection limits obtained for the metal cations and chloride anions were 100 and 10 ppb, respectively. The CE-CCD methodology has been demonstrated to be a versatile technique capable of speciation and quantifying the ionic species generated within artificial pit (a pencil electrode) and crevice corrosion geometries for carbon steels and nickel-aluminium bronze, thus allowing the evolution of the solution chemistry to be assessed with time and the identification of the key corrosion analyte targets for structural health monitoring

The effect of large-area pulsed electron beam melting on the corrosion and microstructure of a Ti6Al4V alloy

The use of titanium alloys in biomedical applications continues to increase due to the excellent stiffness to weight ratio and high corrosion resistance. In order to improve the surface wettability and corrosion properties of a Ti-6Al-4V alloy, the surface treatment method, large area electron beam melting technique was investigated. Polished samples were subject to pulsed treatments of 1, 15 and 25 at 1.38 J/cm2 beam energy. Surface roughness and contact wetting angles were reduced as a result of the treatment. Microstructural analysis of the surface by XRD and FIB-TEM revealed a martensitic alpha prime phase formed as a result of the high cooling rates induced by the treatment. The presence of this homogenous martensite layer was shown to facilitate a compact passive oxide layer formation during corrosion, thus improving corrosion rates by several orders of magnitude compared to an untreated sample. Large area electron beam melting of Ti-6Al-4V induced a number of changes to the near surface microstructure of the samples, all of which could be used to tailor mechanical and corrosion properties to that of a desired application, without compromising the bulk material properties. These are explored in detail in this work

Review of condition monitoring and fault diagnosis technologies for wind turbine gearbox

In order to develop robust condition monitoring and prognosis technologies and systems for wind turbine gearboxes, a comprehensive review of the state-of-art of condition monitoring and fault diagnosis techniques has been carried out. The challenges and opportunities are identified to guide future research in improving the accuracy and ability of condition monitoring and prognosis systems for wind turbine gearboxes. This review also focuses on the fault diagnosis technologies and application of novel sensors in wind turbine gearbox condition monitorin

Self-assembled monolayer protective films for hybrid sliding contacts

Silicon nitride as an energy efficient material is replacing conventional steels for new generation engineering components such as bearings, cutting tools, electronics and engine parts in automotive, aerospace and wind industries. Compared with steel bearings, silicon nitride bearings can be operated at much higher temperatures and speeds with >60% weight reduction and up to 80% friction reduction. These are all due to its unique material properties, including high wear and corrosion resistance, low density and heat generation. Current lubrication solutions for hybrid contacts, where silicon nitride balls and steel races are used, are mostly relying on the protection film formed on the metal surfaces. Self-assembled monolayers (SAMs) have been found very useful in modifying surfaces, especially for microelectromechanical system and nanoscale applications, e.g. atomic force microscopy tips, etc. This study aims to investigate the feasibility of forming a SAM protection film on industrial grade bearing material silicon nitride to reduce the friction for the oil lubricated hybrid contacts. Four silanes with different functional head groups, including octadecyltrichlorosilane (OTS), octyltrichlorosilane, chlorodimethyloctadecylsilane and octadecyltrimethoxysilane, were initially investigated to form SAMs on industrial grade silicon nitride surfaces. The effects of concentration and immersion time of the silanes on the formation of SAMs on the silicon nitride surface were evaluated using contact angle measurements. The preliminary results show that the wetting properties of the silicon nitride surface can be effectively modified by the formation of SAMs from the silane solutions. OTS can form an order and compact SAM on the silicon nitride surfaces within 2 min at the concentration of 2··5 mM in decane solution, while the other three alkylsilanes can also effectively modify silicon nitride surfaces given sufficient immersion time, e.g. over 1 h. Tribological tests were subsequently carried out on a ball on disc rig where a steel ball and a silicon nitride disc were used. The effect of the formation of alkylsilane SAMs on the friction between the sliding contacts has been evaluated in two different methods. The first method was to test preformed SAM films under dry conditions, and the second was to premix one of the surfactants with Shell Vitrea ISO 32 mineral base oil and then spray the mixture to the contacts during the ball on disc testing. The test results show that an average of over 40 and 30% friction reduction was achieved for the hybrid contact when lubricated with the base oil mixed with OTS (>2··5 mM) and octadecyltrimethoxysilane (5 mM) respectively compared with that of the sliding contact lubricated by the base oil only. Since OTS may produce corrosive byproducts during SAM formation, octadecyltrimethoxysilane may be a more suitable additive for the hybrid contact